$ D = \left[\begin{array}{rr}4 & 2 \\ 3 & 4 \\ 3 & 4\end{array}\right]$ $ C = \left[\begin{array}{rrr}-1 & 2 & 3 \\ 1 & -2 & 0 \\ 1 & 2 & 1\end{array}\right]$ Is $ D+ C$ defined?
In order for addition of two matrices to be defined, the matrices must have the same dimensions. If $ D$ is of dimension $( m \times  n)$ and $ C$ is of dimension $( p \times  q)$ , then for their sum to be defined: 1. $ m$ (number of rows in $ D$ ) must equal $ p$ (number of rows in $ C$ ) and 2. $ n$ (number of columns in $ D$ ) must equal $ q$ (number of columns in $ C$ Do $ D$ and $ C$ have the same number of rows? Yes Yes No Yes Do $ D$ and $ C$ have the same number of columns? No Yes No No Since $ D$ has different dimensions $(3\times2)$ from $ C$ $(3\times3)$, $ D+ C$ is not defined.